Boreholes, which are also commonly referred to as “wellbores” and “drill holes,” are created for a variety of purposes, including exploratory drilling for locating underground deposits of different natural resources, mining operations for extracting such deposits, and construction projects for installing underground utilities. A common misconception is that all boreholes are vertically aligned with the drilling rig; however, many applications require the drilling of boreholes with vertically deviated and horizontal geometries. A well-known technique employed for drilling horizontal, vertically deviated, and other complex boreholes is directional drilling. Directional drilling is generally typified as a process of boring a hole which is characterized in that at least a portion of the course of the bore hole in the earth is in a direction other than strictly vertical—i.e., the axes make an angle with a vertical plane (known as “vertical deviation”), and are directed in an azimuth plane.
Conventional directional boring techniques traditionally operate from a boring device that pushes or steers a series of connected drill pipes with a directable drill bit at the distal end thereof to achieve the borehole geometry. In the exploration and recovery of subsurface hydrocarbon deposits, such as petroleum and natural gas, the directional borehole is typically drilled with a rotatable drill bit that is attached to a working end of a bottom hole assembly or “BHA.” A steerable BHA can include, for example, a positive displacement motor (PDM) or “mud motor,” drill collars, reamers, shocks, and underreaming tools to enlarge the wellbore. A stabilizer may be attached to the BHA to control the bending of the BHA to direct the bit in the desired direction (inclination and azimuth). The BHA, in turn, is attached to the bottom of a tubing assembly, often comprising jointed pipe or relatively flexible “spoolable” tubing, also known as “coiled tubing.” This directional drilling system—i.e., the operatively interconnected tubing, drill bit, and BHA—is usually referred to as a “drill string.” When jointed pipe is utilized in the drill string, the drill bit can be rotated by rotating the jointed pipe from the surface, through the operation of the mud motor contained in the BHA, or both. In contrast, drill strings which employ coiled tubing generally rotate the drill bit via the mud motor in the BHA.
Many conventional drilling motors include a progressive cavity, positive displacement motor (PDM) to provide additional power to the bit during a drilling operation. As an alternative to PDMs, some BHAs will employ a turbine-based motor (or “turbodrill”) to provide the additional power. Both PDM and turbine motors are fluidly driven by the drilling mud pumped down the drill string, through the drilling motor, and out the bit assembly. For example, a typical PDM assembly (also known as a “Moineau motor”) includes a multi-lobed stator with an internal passage within which is disposed a multi-lobed rotor. The PDM assembly operates according to the Moineau principle, where pressurized fluid that is forced through the series of helically shaped channels formed between the stator and rotor acts against the rotor causing nutation and rotation of the rotor within the stator. Rotation of the rotor generates a rotational drive force for the drill bit. Additional information regarding positive displacement mud motors can be found in commonly owned U.S. patent application Ser. No. 12/876,515, which was filed on Sep. 7, 2010, and is incorporated herein by reference in its entirety and for all purposes.
During a borehole drilling operation, the drill bit may become lodged in the earth formation or stuck in debris that has accumulated in the borehole around the BHA. Under such circumstances, it can be difficult, if not impossible, to pull the entire drill string, including the drill bit and BHA, out of the borehole. In arrangements where the drill bit is attached to the lower end of a drill pipe arrangement, the drill pipe can be rotated by the rotary table as an upward (pulling) force is applied to the drill string in an attempt to dislodge the stuck drill bit. In the event that the drill bit cannot be dislodged through rotation of the drill pipe, the drill bit or, in some arrangements, the entire BHA assembly may be separated from the remainder of the drill string (e.g., via a release joint). After the drill string is pulled uphole and removed from the borehole, the abandoned drill bit/BHA can then be “fished” from the earth formation. This process, however, is very time consuming and expensive.
In drill strings with an in-hole motor, such as fluid-driven mud motors, wherein the drill bit is driven, at least in part, by a mud motor interposed between the string of drill pipes and the bit, it is oftentimes not possible to dislodge the stuck drill bit by causing the bit to rotate by rotation of the drill pipe string above the motor. This is so because the reaction torque of such in-hole motors is, generally speaking, taken by a rotary table at the surface of the borehole, whereby the drill pipe string can either be held stationary or, if desired, rotated to obviate the wedging of the string. If the bit becomes stuck, the motor will oftentimes stall such that continued rotation of the bit may not be possible, notwithstanding the availability of additional fluid pressure or, in the case of electrically driven in-hole motors, electromotive force. As a consequence, freeing the drill string often requires the drill pipe string and motor be jarred and pulled from the borehole without rotating the bit.